There are many commercial methods for preparing rotor housings for a typical rotary internal combustion engine. One pertinent method comprehends the preparation of a core surface which is the mirror image of the intended surface of the rotor housing. The core is flame spray coated with a material, such as plain carbon steel, to form a relatively thick and substantially porous self-fused coating on the mandrel. Material selection for the flame spray is limited because the material must attain adherency to the ultimate housing (usually aluminum) which will surround the coating. The spray coating and mandrel together are transferred to a die-casting machine where massive aluminum is cast thereabout to form an integral composite. This is sometimes referred to as the "transplant" method. The mandrel and coating must be preheated prior to introduction to the die-casting machine. Following the complete aluminum die-cast process, the core is stripped from the coating liner to leave an interiorly smooth resultant rotor housing. The principal drawbacks of this known transplant technique are: (a) plain carbon steel, not being adequatly wear-resistant by itself, is only effective as a metallurgical intermediate and the liner must further be processed with an additional wear-resistant coating such as chrome to complete the construction, (b) considerable porosity results from flame spray coating technique thereby reducing heat transfer through the housing to the cooling system disposed about the rotor housing, and (c) the mandrel, being subjected to heating and cooling as a result of being placed within the die-casting process, is subjected to early destruction and the smoothness of its outer surface is prematurely destroyed resulting in eventual defects in the surface of liners requiring additional grinding to remove the defects in the coating liner.
A particularly useful material having high wear-resistance is that of an electrolytically deposited base of nickel with embedded silicon carbide particles. Such material has been known for some time for purposes of coating various products, including rotor housings for rotary engines. However, the technique has involved only direct electrolytic deposition, never by way of the transfer technique mentioned above. A significant problem that may have prevented the prior art from combining the art of electrolytic nickel coating with the transfer method is the inability to obtain an adequate bond. Electrolytic coatings are extremely dense, usually having no porosity. Porosity normally accompanys a sprayed coating providing a basis for interlocking and wetting the cast metal thereto which will withstand the severe environment of a rotary internal combustion engine. The prior art has not appreciated the value and technique of utilizing a wear-resistant material as nickel-silicon carbide in combination with the concept of brother mandrels; an initial mandrel has not been used to define a liner, the first mandrel being then removed from the liner and the liner then being placed on a brother mandrel in the die-cast process.